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Color tunable light source module with brightness and dimming control

  • US 9,794,999 B2
  • Filed: 04/03/2014
  • Issued: 10/17/2017
  • Est. Priority Date: 04/04/2013
  • Status: Active Grant
First Claim
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1. A method of controlling brightness and color temperature in a light source device having a plurality of independently addressable groups of LEDs, wherein the LEDs in each group emit light of a different color, the method comprising:

  • receiving a control signal indicating that a brightness of the light source should be changed from a starting brightness value to a target brightness value;

    defining a brightness trajectory from the current brightness value to the target brightness value, the brightness trajectory consisting of a sequence of frames, each frame having a different brightness value assigned thereto and a duration that is long enough to be perceptible to a human eye; and

    executing the brightness trajectory, wherein executing the brightness trajectory includes, for each frame in the sequence of frames;

    determining, using a microcontroller, a brightness set-point for the current frame based at least in part on the brightness trajectory;

    computing, for each of a plurality of output channels of the microcontroller, a pulse width and a number of pulses to include in a pulse train to be generated on each of the plurality of output channels during a brightness cycle that is common to all of the output channels, the brightness cycle consisting of a fixed number (NB) of pulse periods, each pulse period having the same duration (p), the pulse train on each output channel consisting of a selectable number (NON) of active pulse periods of duration p during each of which a pulse having a selectable pulse width is generated and another number (NB

    NON) of inactive pulse periods of duration p during which a pulse is not generated, the computation being based at least in part on a current color temperature and the brightness set-point for the current frame such that the pulse width for each output channel is computed based on the current color temperature and the number NON of active pulse periods is computed based on the brightness set-point,wherein selecting the number NON of active pulse periods and the pulse width for each output channel includes;

    accessing a lookup table using the current color temperature to determine first and second baseline pulse width parameters;

    interpolating between the first and second baseline pulse width parameters to generate a width value consisting of a first subset of most significant bits and a second subset of least significant bits;

    determining the pulse width based at least in part on the most significant bits of the width value; and

    determining the number NON of pulses to include in the pulse train based at least in part on the brightness set point and the least significant bits of the width value;

    generating, on each of the plurality of output channels, a pulse train using the pulse width and number of pulses computed for that channel;

    converting each of the pulse trains to an operating current;

    delivering each of the operating currents to a different one of the independently addressable groups of LEDs; and

    repeating the acts of generating, converting and delivering for the duration of the frame.

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